1. Technical Field
The present disclosure relates to systems, devices and methods for the treatment of hypothermia. The present disclosure also relates to systems including garments adapted to controllably emit energy for warming the wearer, e.g., to maintain the core body temperature.
2. Discussion of Related Art
Normal body core temperature is controlled within tight parameters to ensure normal metabolism and body functions, such as nervous system function, e.g., the conduction of nerve impulses, and optimal skeletal muscle contraction. Body temperature is usually maintained near a constant level of 36.5° C. to 37.5° C. (98° F. to 100° F.) through biologic homeostasis or thermoregulation. Thermoregulation is the process of maintaining normal core temperature within certain boundaries and involves positive and negative feedback by the brain to minimize variations from normal values or thresholds. If the body is unable to maintain a normal temperature and core temperature decreases below normal levels, a condition known as hypothermia occurs.
Hypothermia is a serious condition in which the core body temperature drops to below the level required for normal metabolism and body functions, generally a temperature of less than 36° C. (96.8° F.), where tissue damage or death may occur. As core body temperature decreases, the basal metabolic rate and oxygen consumption drop. Hypothermia may be classified as mild hypothermia (34° C. to 36° C.), moderate hypothermia (32° C. to 34° C.), and severe hypothermia (below 32° C.).
Hypothermia affects the function of all organ systems. As the core body temperature declines, there can be respiratory depression with resultant hypoxemia and hypercarbia. Hypoxemia refers to a low level of oxygen in the blood. Hypercarbia refers to high arterial carbon dioxide (CO2) levels. A combined respiratory and metabolic acidosis, e.g., high acidity of blood and tissue fluids, may occur due to hypoventilation, CO2 retention, reduced hepatic metabolism of organic acid due to decreased perfusion of the liver, and increased lactic acid production from impaired perfusion of skeletal muscle and shivering. Shivering, if prolonged, may cause hypoglycemia.
Hypothermia contributes to alterations in physiologic functions, and through alterations of the normal coagulation function, can contribute to further hemorrhage (excessive bleeding over a short period of time, either internally or externally) and shock in an injured victim. Severe accidental hypothermia is associated with marked depression of cerebral blood flow and oxygen requirement, reduced cardiac output, and decreased arterial pressure. Hypothermia following exposure with core temperature below 32° C. is associated with high mortality.
Rewarming of hypothermic patients may be undertaken using passive and/or active methods. Active core rewarming techniques are the primary therapeutic modality in hypothermic victims in cardiac arrest or unconscious hypothermic patients with a slow heart rate. Active core rewarming includes external methods of rewarming as well as methods directed at rewarming the core. One simple means of transferring a large amount of heat to the core of victims with moderate to severe hypothermia is the administration of warmed intravenous fluids. External rewarming methods include the use of heat packs; heating blankets, such as warm-air-circulating blankets and warm-fluid-circulating blankets; reflective blankets; and radiant heat shields.
Passive rewarming methods generally include optimizing environmental conditions while allowing the victim's own heat-generating capabilities to restore normal core temperature. Passive rewarming methods used in mildly hypothermic victims and as an adjunct in moderate-to-severe hypothermia include increasing ambient room temperature and blanket coverage.
Avoiding hypothermia in the perioperative environment is an ongoing challenge. Patients can develop hypothermia perioperatively as a result of various factors in the perioperative environment or the thermoregulatory response of the body to anesthetic agents. Inadvertent perioperative hypothermia is associated with serious complications involving circulation of blood, coagulation, wound healing, and drug metabolism.
First and emergency responders, such as prehospital and EMS providers, firefighters, and police officers, and active military personnel must be careful about their own health and physical abilities in order to perform their job functions well. Decreases in core body temperature may reduce work capacity, stamina, cognitive functioning, and efficiency and can lead to individual morbidity and mortality.